1. Field of the Invention
The present invention relates to a positioning apparatus enabled to move a work in, for example, a chamber isolated from external environment.
2. Description of the Related Art
In a semiconductor manufacturing apparatus, a work is processed by being put on a stage and moved in a process chamber, the inside of which is maintained in a vacuum state or in a special gaseous atmospheric state. In the case that a positioning apparatus is provided in the process chamber, there is a fear that lubricant supplied to a moving part thereof may scatter and contaminate the inside of the process chamber.
To solve such a problem, for example, U.S. Pat. No. 4,191,385 discloses an integral negative-pressure-sealed gas-bearing assembly. According to such related art techniques, a moving part enabled to move in two-dimensional directions is provided on a bearing block. Further, a process chamber is formed between the bearing block and the moving part. The process chamber is sealed by a differential pumping seal from external environment. This enables that a work put on the moving part is processed in the process chamber while the process chamber is maintained in negative pressure environment. Consequently, a drive portion for driving a work can be installed outside the process chamber. Thus, the process chamber can be restrained from being contaminated. Moreover, the maintenance of the driving portion is facilitated. U.S. Pat. No. 4,191,385.
Meanwhile, such processing to be performed in a process chamber is applied to a work whose application, for example, fabrication of a semiconductor, requires extremely high precision. Incidentally, an inner surface of a casing may be used as a reference face for processing. However, for instance, when the process chamber is vacuumized, a large force due to the difference in pressure between the inside and the outside of the casing is applied to a casing covering the process chamber, so that minute deformation of the casing occurs. Further, when an opening communicating with the process chamber is made to face the moving block, minute deformation of the moving block itself also occurs, because the inside of the opening is in a vacuum state. In such a case, the deformation of the moving block results in change of the processing reference position serving a reference for processing. Thus, there is a fear that processing cannot be achieved with good accuracy. As a countermeasure against such a problem, it has been devised to suppress the deformation by increasing the thickness of the moving block. However, the increase in the thickness of the moving block causes a new problem in that the entire system gets heavy.
On the other hand, there has been made an attempt to provide a decompression chamber, whose inner pressure is lower than the external pressure of the process chamber, across such a moving block from the process chamber so that the deformation of the moving block is suppressed by bringing the barometric pressure at the side of the process chamber closer to that of the decompression chamber. However, in such a configuration of the system, it is necessary to provide differential pumping seals at both the side of the process chamber and the side of the decompression chamber. Nevertheless, when some trouble occurs at in an exhaust pump for causing the differential pumping seals to operate, and in piping thereof, atmospheric air enters the process chamber P, so that the barometric pressure therein increases. Further, there is a fear that an object being processed may become a defective product.